In recent years, with development of magnetic recording, high image quality and high sound quality have been highly demanded. In order to meet of demand, the particle size of the magnetic substance has been decreased and the density of the magnetic recording medium has been increased. With use of large quantities of magnetic recording media, it is required to produce the medium at low production cost. A technique to meet this requirement is to provide a plurality of magnetic layers. In this case, since the upper layer is provided with characteristics for high image quality and the lower layer is provided with characteristics for high sound quality, a suitable ferromagnetic powder can be used and the density of the medium can be increased. Providing a plurality of magnetic layers has a feature that the medium can be produced at a low production cost because a suitable material can be used depending on the respective layer. It is now believed that in order to increase electromagnetic characteristics, it is effective to improve the characteristics of the surface of the magnetic layer. In the case of magnetic tape, .in order to improve the surface properties of the upper layer, it is necessary to improve the surface properties of the lower layer. The surface properties of the lower layer can be improved by introducing a low molecular weight binder into the lower layer, thereby making the lower layer soft. Thus a multilayer tape can be made having excellent electromagnetic characteristics.
Electromagnetic characteristics of a magnetic recording medium should be evaluated under the provision that the magnetic recording medium exhibits good running performance. In a magnetic recording medium, in order to secure good running performance, it is necessary that the coefficient of friction of the surface of the magnetic layer is low.
Good running performance is secured without deterioration of electromagnetic characteristics by introducing a predetermined amount of lubricant into the upper and lower layers. Running performance of a magnetic recording medium can be secured by the effect of a lubricant present in the surface of the magnetic layer. In the case of an image in a still mode among conditions of use of the magnetic recording medium, addition of a lubricant contributing only to running properties is not always sufficient. It is known that particularly under low temperature conditions, the lubricating effect drops as compared with that at ordinary temperatures. Thus, a lubricant is required to be added in such an amount not only to secure running performance but also to secure still durability of the magnetic layer.
In the conventional methods described in JP-A-60-256917 and 62-31018 (the term "JP-A" used herein means an unexamined published Japanese patent application), and Japanese Patent Application No. 63-49811, fatty acid or fatty acid esters are added, or a difference in amount of ester is produced between two layers. In any case, the results obtained are not satisfactory.
For example, in JP-A-60-2569l7, oleic acid is introduced into both the upper layer and the lower layer of the magnetic layer. In JP-A-62-3l0l8, three components of stearic acid, oleic acid and butyl stearate are introduced into any one of the upper layer and the lower layer. Japanese Patent Application No. 63-49811 discloses that the amount of ester contained in the lower layer is made 1.2 to 3 times that in the upper layer. In any case, however, nearly equal amounts of lubricant are introduced in the upper layer and the lower layer. The lubricant contained in the upper magnetic layer directly contributes to still durability. The lubricant contained in the lower layer is to be fed to the upper magnetic layer and thus is required to be easily mobile. That is, although lubricants to be used in the upper and lower layers are required to have different characteristics, the same kind of lubricant has heretofore been used in both the upper and lower layers and, therefore, characteristics required for both layers are not satisfied at the same time. That is, still durability at the initial stage is not good and still durability after 100 running passes is insufficient.